Hypersensitivity pneumonitis: a diagnostic dilemma.

Hypersensitivity pneumonitis is an important but underdiagnosed form of interstitial lung disease. Its clinical hallmark is recurrent or chronic pulmonary symptoms of variable severity associated with an array of systemic symptoms but without extrapulmonary structural abnormalities. Clinical suspicion is the key to diagnosis, which is supported by establishing an environmental or occupational exposure to a causative inhaled antigen; by excluding infectious and other causes of recurrent, migratory, or progressive radiologic lung abnormalities; and by demonstrating antigen-specific antibodies in the serum. Two cases of hypersensitivity pneumonitis are described that illustrate the widely variable clinical, laboratory, and radiologic presentations and emphasize the importance of diagnosing this treatable condition.